1. Technical Field
An organic anti-reflective polymer which prevents back reflection of lower film layers and eliminates standing wave that occurs as a result of thickness changes of photoresist and light, in a process for fabricating ultrafine patterns that use photoresist for lithography by using 193 nm ArF and its preparation method are disclosed. More particularly, the organic anti-reflective polymer is disclosed that is useful for fabricating ultrafine patterns of 64M, 256M, 1G, and 4G DRAM semiconductor devices. A composition containing such organic anti-reflective polymer, an anti-reflective coating layer made therefrom and a preparation method thereof are also disclosed.
2. Description of the Background Art
In a fabrication process of ultrafine patterns for preparing semiconductor devices, standing waves and reflective notching inevitably occur due to the optical properties of lower film layer on the wafer and due to the thickness change of photosensitive film. In addition, there is another problem of the CD (critical dimension) alteration caused by diffracted and reflected light from the lower film layers. Thus, it has been suggested to introduce anti-reflective coating that enables preventing back reflection at a lower film layer by introducing organic material showing high absorbance at a wavelength range of the light employed as a light source.
Anti-reflective coating is classified into inorganic and organic anti-reflective coating depending upon the material used, or into absorptive and interfering anti-reflective coating based on the operation mechanism. For microlithography using I-line (365 nm wavelength) radiation, inorganic anti-reflective coating is predominantly used, while TiN and amorphous carbon as absorptive system and SiON as interfering system are employed.
In a fabrication process of ultrafine patterns using KrF laser, SION has been mainly used as an inorganic anti-reflective film. However, in the case of an inorganic anti-reflective film, no material has been known which enables the control of the interference at 193 nm, the wavelength of light source. Thus, there has been great deal of efforts to employ an organic compound as an anti-reflective coating.
To be a good organic anti-reflective coating, the following conditions must be satisfied:
(1) Peeling of the photoresist layer due to the dissolution in a solvent must not take place when conducting a lithographic process. In order to achieve this goal, a molded coating must be designed to form a cross-linked structure without producing any chemical as a by-product.
(2) Chemicals such as acid or amine must not migrate into or out from the anti-reflective coating. This is because when acid migrates from anti-reflective coating, undercutting occurs at a lower part of the pattern while footing may occur when a base such as amine migrates.
(3) The etching speed of the anti-reflective coating should be faster than that of the upper photosensitive film so as to facilitate etching process by using photosensitive film as a mask.
(4) Therefore, the anti-reflective coating must be as thin as possible to an extent to sufficiently play a role as an anti-reflective coating.
The existing organic anti-reflective material is mainly divided into two types, specifically, (1) polymers containing chromophore, cross-linking agent (single molecule) cross-linking the polymers and an additive (thermally variable oxidant) and (2) polymers which can cross link by themselves and contain chromophore and an additive (thermally variable oxidant). But these two types of anti-reflective material have a problem in that the control of k value is almost impossible because the content of the chromophore is defined according to the ratio as originally designed at the time of polymerization. Thus, if it is desired to change the k value, it must be synthesized again.